1. Field of the Invention
The present invention generally relates to an image forming apparatus such as a copier, a printer, a facsimile machine, and a multi-function machine including functions of the above, and a fixer included in the image forming apparatus.
2. Discussion of the Background Art
In general, electrophotographic image forming apparatuses include an image forming unit for forming a toner image and a fixer for fixing the toner image on a recording medium.
A fixer includes a fixing member such as a fixing roller, a fixing belt, and a fixing sleeve, and a pressure member such as a pressure roller and a pressing belt. The fixing member and the pressure member are configured to contact each other to form a fixing nip therebetween. A recording medium is transported to the fixing nip, where a toner image on the recording medium is fixed thereon.
In fixers, it is preferable to adjust pressure of the fixing nip according to sheet thickness. Further, a fixing member and/or a pressure member typically include an elastic layer of a foamed rubber to secure a sufficient fixing nip when the diameter thereof is relatively small. When such an elastic layer is used, it is necessary to adjust the pressure frequently to prevent a decrease in hardness, foam breaking, and permanent compression strain of the elastic layer, which may occur when constant pressure is applied to such an elastic layer.
To solve the problems described above, changing the pressure of the pressure member against the fixing member has been proposed.
In one related-art example of a fixer, a pressure roller as a pressure member is pressed against a fixing roller as a fixing member by a pressure lever provided at an axis of the pressure roller. The pressure lever engages a cam and the pressure roller is pressed against or disengaged from the fixing roller when the cam is rotated by a motor.
In another related-art example of a fixer, the pressure of a pressure member on a fixing belt as a fixing member is adjusted to prevent deformation of an elastic layer of the fixing belt.
Yet in another related-art example of a fixer, a pressure member is pressed against a fixing member by rotating a cam. The rotation of the cam is detected with a micro switch that is in contact with the cam.